1. Field of the Invention
The present invention relates to a technology for up or down converting a frequency, and more particularly, to a frequency up and down converter which can up or down convert the frequency of an input signal using an oscillation signal with a frequency lower than an original frequency.
2. Description of the Related Art
In general, in a wireless communication system, in order to improve frequency selectivity characteristics for transmission and reception paths, frequency up and down converters for channels are needed for channel separation in an intermediate frequency (IF) analog frequency stage.
FIG. 1 is a block diagram of a conventional frequency down converter. Referring to FIG. 1, a conventional frequency down converter includes a frequency down conversion unit 110, a local oscillator signal generation unit 120, and a transimpedance amplification unit 130.
The frequency down conversion unit 110 has a single balanced frequency down converting section and a double balanced frequency down converting section. The frequency down conversion unit 110 includes a first mixer 110A and a second mixer 110B.
The first mixer 110A is configured to control and convert high frequency signals RF_INP and RF_INN inputted thereto, into I channel intermediate frequency signals by using local oscillator signals LOA and LOB. The second mixer 110B is configured to control and convert the high frequency signals RF_INP and RF_INN into Q channel intermediate frequency signals IF_QP and IF_QN by using local oscillator signals LOC and LOD.
The transimpedance amplification unit 130 includes a transimpedance amplifier TIA, resistors R1 and R2 and capacitors C1 and C2, and is configured to amplify the I channel intermediate frequency signals outputted from the first mixer 110A using the component elements. Accordingly, amplified type I channel intermediate frequency signals IF_IP and IF_IN are outputted from the transimpedance amplifier TIA.
The local oscillator signal generation unit 120 includes a plurality of local oscillator signal generators 121 to 124. The waveforms of the local oscillator signals inputted to and outputted from the local oscillator signal generators 121 to 124 are shown in FIG. 2.
Referring to FIG. 2, the local oscillator signal generators 121 to 124 receive pulse width modulated type local oscillator signals LO0 and LO270, LO180 and LO90, LO0 and LO90, and LO180 and LO270 with different phases, and generate pulse width modulated type local oscillator signals LOA and LOB, and LOC and LOD with a duty ratio equal to or less than 50% and a phase difference of 180° to be used in the first mixer 110A and the second mixer 110B.
FIG. 3 is a block diagram of a conventional frequency up converter. Referring to FIG. 3, a conventional frequency up converter includes a frequency up conversion unit 310, a local oscillator signal generation unit 320, and a transimpedance amplifier 330.
The frequency up conversion unit 310 has a single balanced frequency up converting section and a double balanced frequency up converting section. The frequency up conversion unit 310 includes a first mixer 310A and a second mixer 310B.
The first mixer 310A is configured to control and convert I channel intermediate frequency signals IF_IP and IF_IN inputted thereto, into high frequency signals by using local oscillator signals LOA and LOB. The second mixer 310B is configured to control and convert Q channel intermediate frequency signals IF_QP and IF_QN inputted thereto, into high frequency signals by using local oscillator signals LOC and LOD.
The transimpedance amplifier 330 is configured to amplify the high frequency signals outputted from the common output terminals of the first mixer 310A and the second mixer 310B and output a positive polarity high frequency signal RF_OUTP and a negative polarity high frequency signal RF_OUTN.
The local oscillator signal generation unit 320 includes a plurality of local oscillator signal generators 321 to 324. The waveforms of the local oscillator signals inputted to and outputted from the local oscillator signal generators 321 to 324 are shown in FIG. 2.
Referring to FIG. 2, the local oscillator signal generators 321 to 324 receive local oscillator signals LO0 and LO270, LO180 and LO90, LO0 and LO90, and LO180 and LO270 with different phases, and generate local oscillator signals LOA and LOB, and LOC and LOD with a duty ratio equal to or less than 50% and a phase difference of 180° to be used in the first mixer 310A and the second mixer 310B.
In the conventional frequency down converter, when converting high frequency signals into intermediate frequency signals, local oscillator signals with a frequency corresponding to the frequency of the high frequency signals to be converted are used. In this regard, as a mobile communication system recently trends toward the use of a higher frequency signal, it is difficult to provide local oscillator signals with a correspondingly high frequency.
Also, in the conventional frequency up converter, when converting intermediate frequency signals into high frequency signals, local oscillator signals with a high frequency corresponding to the frequency of the intermediate frequency signals are used. In this regard, as a mobile communication system recently trends toward the use of a higher frequency signal, it is difficult to provide local oscillator signals with a correspondingly high frequency.